1. Field of the Invention
The present invention generally relates to an image scanning apparatus used in an image forming apparatus such as a copy machine, a facsimile machine, etc., and more particularly to an image scanning apparatus having a contact-type image sensor to scan an original image.
2. Description of the Background Art
A CCD image sensor or a contact-type image sensor is commonly used in an image scanner.
In an image scanner applicable for scanning a book document as an original document which has a fixed position on a contact glass, a thickness of the image scanner can be reduced by using a contact-type image sensor rather than a CCD image sensor. Additionally, usage of the contact-type image sensor has advantages that a driving system thereof is greatly simplified such that many adjustments are not needed, and a distortion of an image is reduced due to an optical reduction system.
However, although the contact-type image sensor has the above-mentioned advantages, there is a problem in that a constant position of a focal point is not obtained over an entire scanning area unless a supporting construction of the image sensor has a high accuracy and rigidity.
An image scanner may also include an automatic document feeder (ADF), which feeds documents one by one. Each document fed into the ADF is conveyed to a scanning point at which point the document is scanned by an image reading apparatus, and then the document is conveyed to an outside of the ADF.
As an example, a background device of FIG. 1, which is disclosed in Japanese Laid-Open Patent Application No. 4-369162, discloses an image scanner having a contact-type image sensor and two contact glasses 1A, 1B. One contact glass 1B is placed at a bottom to one side on a main body, and another contact glass 1A is placed at another side of the main body. In this case, each contact glass 1A, 1B is placed separately so that there is a problem that a bump and nip exist between the two contact glasses 1A and 1B, or between the contact glasses 1A, 1B and a supporting member for supporting the contact glasses 1A, 1B. As a result, there is a difficulty of manufacturing such a device with accuracy and rigidity, and a supporting construction may be scratched by the bump and nip and thereby cannot function normally as a spacer.
A background device of FIG. 2, which is also disclosed in Japanese Laid-Open Patent Application No. 4-369162, discloses an image scanner having a contact-type image sensor and a single contact glass 1C. The image scanner has a guide member 100 about a scanning point inside the ADF which guides an original document that is scanned smoothly by an image sensor for an outlet of the ADF. Moreover, a part of the guide member 100 is imbedded in the contact glass 1C. By requiring this guide member 100 to be imbedded in the contact glass 1C, manufacturing processes are increased, and thereby a cost increases. Further, in this device the ejecting path is formed in a U-shape and the guiding member 100 guides an original document scanned in a slanting direction upward, and as a result it is possible that the original document may be caught in the ejecting path.
A background device of FIG. 3, which is also disclosed in Japanese Laid-Open Patent Application No. 4-369162, discloses an image scanner having a contact-type image sensor and a single contact glass 1. Moreover the image scanner has a transparency board 200 on a contact glass 1 and successively a film (e.g. mylar) 201 and a guide member 202. These elements operate to guide a document scanned by an image sensor smoothly for an outlet of the ADF. However, in this device of FIG. 3 the transparency board 200 needs to be set on the contact glass 1 exactly and the film 201 needs to be set downstream of the transparency board 200 exactly. On this account, a component count number and a structure manufacturing process number are increased, and thereby a cost increases. Furthermore, despite establishing the guiding member 202, the transparency board 200 and the film 201, a paper jam may occur, because the ejecting path is in a U-shape and the guiding member 202, the transparency board 200 and the film 201 guides an original document scanned in a slanting direction upward, so that the original document may be caught in the ejecting path.